Embodiments of the present invention relate to a non-volatile semiconductor memory device, and more particularly to a three-dimensional (3D) non-volatile memory device including a U-shaped channel structure.
A non-volatile memory device is a memory device capable of preserving stored data even when not powered. Various non-volatile memory devices such as flash memories have been widely used.
Since the integration enhancement of a two-dimensional (2D) non-volatile memory device in which a single-layered memory cell is formed over a semiconductor substrate is limited, there has been recently introduced a 3D non-volatile memory device in which memory cells are formed along a channel layer vertically protruding from the semiconductor substrate.
3D non-volatile memory devices are largely classified into a first type of 3D non-volatile memory device having a line-shaped channel layer and a second type of 3D non-volatile memory device having a U-shaped channel layer. A 3D non-volatile memory device having the line-shaped channel layer includes a bit line and a source line respectively formed above and below stacked memory cells. A 3D non-volatile memory device having the U-shaped channel layer includes a bit line and a source line, both of which are disposed over stacked memory cells. The 3D non-volatile memory device having the U-shaped channel layer includes a single-layered selection gate, such that it may have a higher degree of integration than the 3D non-volatile memory device having a line-shaped channel layer.
However, the 3D non-volatile memory device having a U-shaped channel layer is formed by stacking a plurality of small-width word lines, so that the stacked structure of the word lines is susceptible to being tilted. In addition, slits must be formed not only between a source side channel and a drain side channel that construct a single channel, but also between neighboring channels, so that the each of the slits has a narrow width, and an etching process has a high level of difficulty. Moreover, as the integration degree of a semiconductor device gradually increases, the number of stacked word lines also increases, so that the above-mentioned problems become more challenging.